Passively stuck: death does not affect gecko adhesion strength

Abstract

Many geckos use adhesive toe pads on the bottom of their digits to attach to surfaces with remarkable strength. Although gecko adhesion has been studied for hundreds of years, gaps exist in our understanding at the whole-animal level. It remains unclear whether the strength and maintenance of adhesion are determined by the animal or are passively intrinsic to the system. Here we show, for the first time, that strong adhesion is produced passively at the whole-animal level. Experiments on both live and recently euthanized tokay geckos (Gekko gecko) revealed that death does not affect the dynamic adhesive force or motion of a gecko foot when pulled along a vertical surface. Using a novel device that applied repeatable and steady-increasing pulling forces to the foot in shear, we found that the adhesive force was similarly high and variable when the animal was alive (mean + s.d. ¼ 5.4 + 1.7 N) and within 30 min after death (5.4 + 2.1 N). However, kinematic analyses showed that live geckos are able to control the degree of toe pad engagement and can rapidly stop strong adhesion by hyperextending the toes. This study offers the first assessment of whole-animal adhesive force under extremely controlled conditions. Our findings reveal that dead geckos maintain the ability to adhere with the same force as living animals, disproving that strong adhesion requires active control.

Nonlinear variation in clinging performance with surface roughness in geckos

“…The gekkotan adhesive system has evolved to enable the exploitation of inclined and inverted surfaces on rocks, or vegetation, with recent expansions onto man‐made structures by some species (Glossip & Losos, ; Gamble et al, ; Hagey et al, ; Ruibal & Ernst, ). The mechanism and dynamics of adhesion, however, have almost exclusively been examined using a variety of smooth (Autumn et al, ; Gillies & Fearing, ; Irschick et al, ; Peressadko & Gorb, ; Russell & Johnson, ; Stewart & Higham, ) and very fine‐grained man‐made surfaces (i.e., glass, Teflon, variations of polyethylene, polyvinyl chloride, aluminum bonding wire, acrylic, and acetate sheets; Campolo, Jones, & Fearing, ; Gillies & Fearing, ; Huber, Gorb, Hosoda, Spolenak, & Arzt, ; Meine et al, ; Persson, ; Persson & Gorb, ; Pugno & Lepore, ; Vanhooydonck, Andronescu, Herrel, & Irschick, ; Winchell, Reynolds, Prado‐Irwin, Puente‐Rolón, & Revell, ), most of them not encountered by geckos under natural conditions. Such research has revealed that geckos perform better on substrates that are smooth, clean, and have uniform surface chemistry (Stark et al, ), apparently because these substrates provide a greater surface area with which setae can make contact (Russell & Johnson, ; Vanhooydonck et al, ).…”

Geckos decouple fore- and hind limb kinematics in response to changes in incline

“…The adhesive system of geckos is an innovation that permits the occupation of ecological niches that were not previously available, thus allowing them to extensively radiate [ 32 ]. Gecko adhesion is very strong [ 33 , 34 ] and achieved through close contact between the surface and setae on the ventral surface of the toes [ 35 – 37 ]. This close contact results in van der Waal interactions [ 38 ], frictional forces [ 39 ] and contact electrification [ 40 ], which collectively result in adhesion.…”

Leaping lizards landing on leaves: escape-induced jumps in the rainforest canopy challenge the adhesive limits of geckos

“…Using nine individuals (5.8-18.3 g) collected in the field in French Guiana [3], we quantified maximum clinging force (F adhesion ) using a portable force transducer, as detailed in previous studies [3,39] (table 2). Briefly, a portable load cell (Mark-10 Series 5 force gauge), sensitive to 50 N, was attached to a small rectangular piece of acrylic glass, onto which the gecko's forelimb was placed and the gecko pulled away from the transducer as a slow and steady rate.…”